1. Field of the invention
The present invention relates to an insulated electric wire with partial discharge resistance and a composition for manufacturing the same, and more particularly to an insulated electric wire with partial discharge resistance including a rubbery modifier in an insulating base resin, the rubbery modifier being capable of improving flexibility of an inorganic insulator and an insulated electric wire, and a composition for manufacturing the same.
2. Description of the Related Art
In a deterioration mechanism for partially discharging an electrical insulator such as coating materials for an electric wire, charging particles generated by a partial discharge may collide with an insulator, high molecular weight chains in the insulator may be broken by the collision, and thermal decomposition may be initiated due to local increase of temperature. Also, chemical deterioration of the insulator may be caused by ozone generated by the partial discharge. It has been known that the partial discharge caused by usage of electrical and electronic appliances, or various deterioration factors derived from other factors combinationally act to raise various barriers to essential functions of the electric insulator. Meanwhile, it has been known that deterioration by partial discharge generated in an inverter controller widely used in recent years is caused by a switch pulse generated by a high voltage surge, which eventually deteriorates coils in the inverter controller.
Accordingly, U.S. Pat. Nos. 4,493,873, 6,100,474, etc. propose an improvement of materials constituting an insulator to prevent or reduce deterioration of the electric insulator by partial discharge. That is to say, U.S. Pat. No. 4,493,873 proposes an inorganic insulator such as oxides or nitrides of inorganic materials, glass, mica and the like as an insulator which is not easily deteriorated by partial discharge, and U.S. Pat. No. 6,100,474 proposes a method for mixing a mixture of silica (SiO2) and chromium oxide with a resin, coating an insulated electric wire with the resultant mixture and reductively calcining the mixture. Meanwhile, it has been known that, regardless of the inorganic insulator and the method as described above, an insulated electric wire having an excellent partial discharge deterioration-resistance is manufactured by applying an insulating paint compound prepared by dispersing fine particles of an inorganic insulator such as silica, alumina (Al2O3), titania (TiO2), etc.
The partial discharge resistance may be improved as the content of the fine particles of inorganic insulator increases among insulators in the insulated electric wire. However, an insulated electric wire, made of an insulated film containing a large amount of the fine particles of the inorganic insulator, also has a disadvantage that its physical properties such as flexibility, pliability, bendability, elongation, etc. may be deteriorated. As described above, if an electrical coil was formed of the insulated electric wire having the deteriorated physical properties such as flexibility, pliability, bendability, elongation, etc., crack occurrence is increased upon coating the insulated electric wire, and therefore the partial discharge resistance of the insulated electric wire is not sufficiently improved due to the crack occurrence.
In order to solve the above-mentioned problems, there has been recently proposed a method for manufacturing an insulated electric wire having a multi-layered structure. The insulated electric wire having the multi-layered structure may be adopted for different purposes in separate layers. That is to say, an insulation layer dispersed with the inorganic insulator has been adopted to improve partial discharge deterioration, and other insulation layers have been adopted to improve physical properties such as flexibility, pliability, bendability, elongation, etc. However, in the case of the insulated electric wires having the multi-layered structure, a thick wire having a diameter of at least 1.5 mm still has a problem that cracks occur in an abruptly bent region of an insulated film upon winding. As an alternative to solve the problem, Japanese Patent No. 496633 proposes a technique for improving flexibility by dispersing a solution of nano-sized inorganic oxide in a solvent to prepare a colloid sol, and mixing the colloid sol with an insulating paint, and U.S. Pat. No. 6,734,361 proposes a method for improving flexibility by chemically combining silica with a resin itself. However, it is difficult to completely solve the above problems of the thick wire having a diameter of at least 1.5 mm by means of the conventional methods.
Accordingly, there have been ardent and steady attempts to develop an insulated electric wire with partial discharge resistance while exhibiting a sufficient pliability even in a thick wire having a diameter of at least 1.5 mm in the related art, and therefore the present invention was designed based on the above technical background.